Process of melting scrap metal.



, UNITED. STATES PATENT OFFICE.

ALBERT E. GREENE, OF CHICAGO, ILLINOIS, ASSIGNOR TO AMERICAN ELECTRICSMELT- ING AND ENGINEERING COMPANY, OF ST. LOUIS, MISSOURI, ACORPORATION OF MISSOURI.

PROCESS OF MELTING SCRAP METAL.

1 ,185,394. Specification of Letters Patent.

No Drawing.

trically melting scrap metal and particu-.

larly steel scrap.

The object of my invention is to provide a method of melting scrapmetal, and in particular steel scrap containing easily oxidizableelements, to produce a metal free from oxid and sound when poured, andto accomplish such results with a minimum loss of the metalconstituents. One of the chief causes of wildness and blow-holes insteel is the presence of oxids of iron or manganese dissolved orcombined with the molten metal, and these oXidS are so readily absorbedby the metal from a slag or from exposure to oxidizing atmosphere, thatvery small amounts of oxygen serve to cause wildness. The longer theexposure to oxidizing conditions, the more costly the remedial treatmentand the more uncertain willbe the result when the oxids are not actuallydisposed of. I have discovered that soundness and deoxidation in steelwhen poured may be practically insured by means of special treatment ofthe metal during the melting process this treatment consisting primarilyin providing a fluid slag and in subjection of this slag to speciallycontrolled reducing action. The processes heretofore in use for themelting of such scrap provide no means. or el e very inadequate means,for preventing oxidation or for insuring the removal of the dissolvedoxids and causes of wildness of the metal during process of melting..-The usual remedy for dissolved oxids is to add deoxidizing alloys likeferrosilicon and ferro-manganese at the time of tapping the heat so thatthere will be as little time as possible for the absorption again ofmore oxids from the slag. Such treatment is" nece sarily uncertain b thas to the amount of dooxidation and as to the amount of alloved metalleft to meet the specifications. One method suggested is the use of aslag to minimize the effect of an oxidizing atmosphere on the steel; buta slag is an excellent carrier of oxygen from atmosphere above metal byoxidation. Another means suggested is the use of a closed furnace having.a neutral atmosphere which will be beneficial to the metal; but thismeans is impracticable and inadequate. If no oxygen entered the furnaceon the scrap charged or through the openings into the furnace thissuggestion would be more plausible; but the entrance into the furnace ofoxid on the scrap is one of the working conditions which my presentinvention is designed. to meet. Oxygen is invariably present on scrapcharged and oxygen enters with the scrap at the time of charging.- Underthese conditions if the furnace is closed, absolutely, and the meltingcaused to proced, the atmosphere which would result would be neutral andlikewise the slag but oxid of iron wouldbe present and would be taken upby the molten metal under these so-called neutral conditions and lossesof metal and time and energy would occur which it is the object of mypresent invention to avoid. The oxid which enters on the scrap willalone rapidly form anoxidizing slag and in actual practice the closingof the furnace and allowing the conditions to become neutral, even ,ifindefinitely prolonged, will not cause reduction of the oxids so as toavoid the necessity of finally deoxidizing the steel. It is to be notedfurther that the entrance of cold air into the furnace is especiallyobjectionable for the reason that the entering air, being cold,displaces the hot gases above the bath and the air spreads out over thecharge so that fresh oxygen is carried to the metal either directly, incase the metal surface is exposed, or else through the slag as a carrier. It should be remembered that carbon monoxid, a reducing gas, maybe formed as a product of the reaction between oxid of iron in the slagand carbon in the metal, but the existence of this reaction does notdeoxidize the steel nor does the reaction product, carbon monoxid,because the reaction does not complete itself; and the carbon monoxidformed tendsto rise toward the roof of the furnace chamber particularlyif cold air from outside the furnace enters.

'It is quite common to see small flames of Patented May 30, 1916.Application filed January 23, 1911. Serial No. 604,013.

in the atmosphere next above the slag is partial evidence of thepresence of suflicient oxygen to support combustion. Further evidence ofthe nature of the atmosphere in electric furnaces of the arc type may behad when it is remembered that usually from 5 to 10 pounds of carbon isburned in the atmosphere of the furnace per ton of steel melted, andthat in the processes as heretofore practised deoxidizing alloys arepractically invariably employed.

Ihe above are the conditions which it is the object of my presentinvention to cornd the slag kept in reduced condition so as to preventabsorption of oxygen by the metal all as provided for in my presentinvention, then it will be necessary to resort to some remedial coursewith material loss in metal, time and energy.

The details of slag composition andtreatment contemplated by my processwill be de-- scribed later.

If the scrap be melted in an open hearth furnace, the oxid commonlypresent on the surface of the scrap forms a slag which reacts with themetal and oxidizes the more readily oxidizable metals. In certain casesthis oxidation has been taken advantage of for removing such impuritiesas phosphorus, namely in the basic open hearth process, but the less ofthe alloy constituents is exaggerated by such procedure. These slags inthe open hearth process take up especially the silicon and themanganese, so that additioins. of these elements have to be made at theend of the heat. Even inthe electric furnace, if a charge of steel scrapbe melted,

the oxids collect as a slag and ordinarily cause a great loss of suchalloy metals as manganese and silicon. My invention is designed toprevent this loss and to avoid the injurious efi'ects of dissolved oxidsresulting from the ordinary process of melting.

Thus a primary feature of my invention is the means of prevention ofinjurious effects during the melting of steel scrap rather than a meansof remedying ill effects after they have occurred,

My invention. contemplates a process of melting scrap metal. in anelectric furnace and preventing excessive loss of metal from oxidationby the use of a slag from which the ingredients of the metal are keptreduced and by which oxidation of the metal is prevented ,by the actionof a reducing agent to which the slag is subjected.

My invention further contemplates the use ofaslag during the meltingsuch as will most readily aid in the saving and deoxidizing of the metalthus in the melting of the metal of basic nature,such as manganesesteel, in a basic'lined furnace, the slag is made essentially of limewith a suitable amount of silica to give it the desired fluidlty; and inthe melting of a metal of essentially acid nature which may be carriedout In melting ordinary steel scrap contain-,

ing, for example, .7 0% manganese and .35 silicon in the usual mannereither in an'electric furnace or in an open hearth furnace, themanganese and the silicon are practically entirely oxidized out of themetal. My present invention enables one to melt steel scrap and keep agiven alloy ingredient at practically the same percentage.

In melting nickel steel scrap or nickelchrome steel scrap, as forexample, armor plate scrap, by the usual processes, 'thereis a strongtendency to produce metal which contains oxids and which, when poured,is wild and will have blow holes in the castings. even though aconsiderable amount of the nickel and possibly some of the chromium maybe retained during the melting. I attribute this tendency towardwildness to the oxids absorbed by the metal during melting, and I findthat by using the process bf this invention a metal is produced which isnot wild, which does not have blow holes, and furthermore which has notsustained a great loss of its constituent metals during melting.

I will now describe my invention in several of its applications, andwill consider first the melting of ordinary steel scrap containing, forexample, carbon 25%, silicon 35% and manganese .70%.- For melting thisrade of scrap I preferably use a basic electric furnace, and either melta small amount of steel therein or else charge a small amount of moltensteel into the furscrap is remelted the sand adhering to the scrap maybe allowed to enter with the scrap and will aid in making a fluid slag.Fluidity of the'slag in'my present invention is important since then theslag readily covers the whole bath of molten metal and makes possiblequick reducing action on the oxids that collect in the slag. A fluidslag also serves to keep a solid carbonaceous reducing agent fromcontact with the steel and therefore to prevent recarburizing of themetal, but it is necessary to provide the reducing agent in reasonablyfine condition so that chunks do not dip through the slag into thesteel. A slag consisting almost entirely oflime requires considerabletime and power to melt it when free from oxid of iron and the like andsuch a slag, by reason of its viscous nature is diflicult to remove fromthe furnace. tofore to rake such a slag out of the furnace. However, bythe provision of silica in combination with the lime as in my presentinvention ample fluidity can be insured and the slag may be pouredthrough a small tap hole from the furnace along with the steel. Inpractising my present invention it is preferable to provide a slag thatwill be fluid enough to keep the molten metal covered so that uponaddition of scrap the surface of the metal bath will not be leftexposed. I then begin to charge the steel scrap, preferably withouttaking the power off the furnace, and at intervals I throw fine coke ontop of the slag either alone or mixed with some of the slag makingmateriaL This reducing agent reduces the oxids of the metals in thescrap and also prevents their further formation. During the melting ofthe scrap, fine coke or other form of reducing agent is further added,as conditions require, to keep the slag reduced. In this way the siliconand the manganese and the iron may be practically prevented fromoxidation, and as a result the usual melting loss may be practicallyavoided and the final additions, commonly made, greatly diminished inquantity.

\Vhen the slag is reduced so as to be practically free from oxid of ironthe steel is then in deoxidized condition and is ready to pour as soonas the temperature is properly regulated. The amount of coke or otherfine carbonaceous reducing agent necessary to bring the slag to thereduced condition is dependent on how much oxids enter with the chargeand have to be reduced, but inasmuch as the slag will, when properlymade, prevent the fine reducing agent from.

carburizing the metal sufficient coke may be added so that it remains onthe surface of the slag after the oxids of the scrap or of metalsdesired reduced have been reduced. The color of the slag will give someidea of how far reduction has proceeded: and when the oxids of iron andmanganese are largely reduced out of the Slag its color will be a. lightgreen or gray or brown. The oxide which enter with the scrap requiretime to collect in the slag and to be reduced. The fluid slag providedfor collects these oxids rapidly and enables the reducing agent to actrapidly on them. When part of a charge has been melted and more ischarged the fluid slag keeps the melted metal covered. If the wholesurface of the bath is covered by the added scrap a little time isrequired to melt the scrap into the bath before adding coke or otherreducing agent to the slag. By making the additions of coke a littletime before melting of the scrap is complete the reduction of the slagmay It has been customary, herebe completed by the time the metal is allraised to pouring temperature, and thus avoid delays in deoxidizingatthe end of the process.

The composition of the lime-silica slag adjusts itself more or lessautomatically and thus, in a basic lined furnace, the slag may take upmagnesia and alumina from the furnace lining to increase the ratio ofbasic ingredients; and the reduction of silica from the slag by means ofcoke may lessen the amount of silica in a slag. It is desirable tocontrol the proportions of basic and acid ingredients in the slag soasnot to undesirably wear the lining. An essential difference between mypresent invention and the commonly practised electric furnace processesis that in the latter oxids of manganese and iron are especially reliedupon to provide fluidity of slam Another feature of my invention is thatcalcium carbid is not so likely to form and the slag is consequentlyeasier to work.

The ability to retain the metals reduced makes it possible to pour olf aportion of a heat and then proceed with melting again without having tolose the alloyed ingredients of the steel and to replace them. In otherprocesses it is customary to rake off the oxidizing slag and when thisis done much valuable alloy metal is lost in the condition of oxid. Ihave also found that by adding scrap and reducing agent at intervals themelting of the scrap and the reduction of the slag are facilitatedbecause the metal added in smaller quantities comes in better contactwith the slag and is more quickly acted on.

Instead of using coke or other solid form of carbon as a reducing agent,I may use a reducing gas such as producer gas, and I have found thatsuch gas will readily and rapidly reduce the oxids out of the slag.

Another application of my process is-to the melting up of silicon steelscrap. I prefer. when melting scrap containing much of acid elementslike silicon. tungsten, etc., to use an acid lined furnace. The furnacemay be started as described above for melting ordinary scrap. The slagis then provided and preferably contains more than 5)? silica. The othercomponent of the slag may consist of lime or any other oxid or oxids ofbasic nature with respect to silica which will form a fluid slag withthe silica under the reducing conditions maintained, but not basic oXidslike iron or manganese which it is desired to reduce. The object ofproviding an oxid of opposite nature to the silica is two fold: first toproduce fluidity; and second. to satisfy the aflinity of silica for abasic oxid so that the oxids of the metals in the steel may be easilyreduced from the fluid slag. It is easier to reduce iron or manganeseoxids held or disclay.

I solved in a silicate slag in which the afiinity of silica islargelysatisfied by a basic oxid other than of iron or manganese than itwould be to reduce an iron silicate or a manganese silicate in theabsence of some other oxid having aflinity for the silica. Sand may beused to make slag and if impure sand is used it is likely to containoxids which will make it easily fusible, such as After the slag isformed fine coke or other reducing agent is thrown on the slag and theoXids of iron and the metals desired reduced are reduced. During themelting of the remainder of the scrap metal reduc-;

ing agent may be added at intervals and at any rate after the lastcharge of scrap has been made. The. action of the reducing agent may becarried on until silica is reduced to metallic silicon which latterenters the metal. This action gives. insurance of deoxidized metal. Thecomposition of the slag is kept approximately uniform more or lessautomatically. Although an acid lined furnace is preferred a furnacelined with any kind of material sufiiciently refractory K and such aswill not undesirably carburize the metal may be used. When theaflinities of the acidic and basic oxids in the slag are more or lesssatisfied by each other, the reduction of the metallic oxids like thoseof iron and manganese is simplified and the action on the refractorylining is not detrimental.

An important feature of my invention is the use of a slag madeessentially of lime and silica to give low melting point, fluid slagfrom which the reduction of metallic oxid and in certain cases of thesilica is accomplished by the reducing action of the added reducingagent. The silicon reduced from such slags enters the metal. Thestrong'reducin action and the helpful fluidity are very lmportant meansof thoroughly deoX- idizing and purifying the steel. This featureapplies in either acid or basic lined furnaces and to slagsin which the'main ingredient may be either acid, like silica in combination with ab51810 ingredient like lime; or to slags in which the main ingredient islime with silica to give the desired-fluidity.

In melting nickel steel scrap or nickelchrome steel scrap by thisprocess, I prefer to employ an acid lined furnace, though a basic linedfurnace may be employed. The process as applied to such scrap is thesame as that described above for ordinary steel chrome steel scrap. Ifirst provide a bath of moltensteel in an acid lined electric furnace,and the amount of this steel may be only a small portion of the totalcharge the furnace is'to hold after the melting in of the scrap. Thisinitial charge may contain, by analysis: carbon 15%, silicon 30%. ifthen provide the charge with an acid slag containing about 80% silicaand a small amount of lime, to produce suitable fluidity in the slag.The tungsten-chrome steel scrap is then charged into the bath while theelectric power is kept on, and during the melting I keep the oxidsreduced out of the slag as described above. After melting all the scrapI prefer to make th final additions to bring the bath to the requiredcomposition, that is, to make up for the lack of alloy metals in theinitial charge of steel and at this time I prefer to regulate the carbonin the steel by means of the tungsten or other alloy additions. Myinvention serves to conserve these additions.

As explained above it is usually advantageous to use a furnace whoselining is of similar nature to the oxid of a particular metal to bereduced from the slag; thus in getting silicon into steel during meltingand retaining it in the steel, a furnace lined with sgllic'ious materialand a slag in which silica 7 tained in the metal as well as manganeseand can be reduced from the slag. I may, however, where desired aim toretain in the steel melted a single alloying metal like manganese andthen add silicon in the form of some alloy at the end of the meltingprocess after the oxid of iron has been reduced from the slag; or I mayretain silicon or some other alloying metal and add others at the end ofthe process. The process is applicable to the melting of any grade ofscrap iron irrespective of its carbon content and the process is notlimited to that group of iron alloys ordinarily known as steel.

The process of this invention is applicabl to the usual types ofelectric melting furnaces, including electric cupula furnaces, it

being essential to maintain the slag reduced through which the scrap ormelted metal passes. a

It is to be understood that my invention 18 applicable to the melting ofsuch metals as aluminum, copper, and metals in general, sub ect to inunous oxidation or change of composition during melting.

The advantages of my present invention.

may be briefly summarized thus:-A slag is provided which is fluid andfrom which oxids of metals desired in the reduced metal steel inessentially'deoxidized condition and containing practically all themanganese which collects in the slag without undesirable carburizing ofthe steel.

6. The method of protecting steel from oxidation and from loss of analloyed element contained therein, while melted in an electric furnace,the process consisting in maintaining a fluid slag covering over thesteel comprising lime and silica in suitable proportion. to givefluidity without undue corrosion of the furnace lining and meantimeadding to the slag a carbonaceous reduoing agent in fine form, andcontinuing the reducing action until the oxid of iron is practically allreduced.

7. The process of making steel from pure scrap materials suitably freefrom impurities not desired in the steel, the process consisting inproviding an electric furnace with a refractory lining containing silicaand of essentially acid nature, melting the scrap therein and providinga slag containing silica together with a basic oxid to give the slagfluidity, this basic o-Xid being of such nature as Will not be reducedmaterially un der the reducing treatment of the process, and meantimeadding a reducing agent to the slag and continuing the treatment untilthe oxid of iron'is practically all reduced from the slag and untilsilicon is reduced.-

8. The method of melting scrap iron in an electric furnace having anacid lining, the process consisting of providing a slag containingsilica and a small proportion. of an oxid basic with respect to silicato give fluidity to the slag, this oxid being one Which will notmaterially reduce under the action of a carbonaceous reducing agent,melting the scrap and keeping the bath covered with this slagand addinga carbonaceous reducing agent to the slag until oxid of iron ispractically all reduced out of the slag and until silicon is reducedfrom the silica of the slag and incorporated in the metal.

'9. The process of melting steel scrap and controlling the carboncontent thereof which consists in providing in an electric furnace aslag comprising acid and basic oxids like silica and lime, theproportions being regulated to produce a fluid slag Without undue Wearon the lining, charging scrap and a carbonaceous reducing agent atintervals, reducing the oXld of iron from the slag so as to prevent itfrom oxidizing meaeea.

the carbon in the-steel and maintaining the desired content of carbon inthe steel Without undesirable carburizing and continuing the reducingaction on the slag until the oxid of iron is practically all reduced outof it, the other alloy constituents being regulated at the end of theprocess.

10. The process of melting steel which consists in providing a suitableelectric furnace and a bath of molten steel therein under a fluid slag,the slag-comprising basic and acid oxids like lime and silica inproportions to give fluidity without undue wear on the lining, chargingscrap and carbona 11. The method of treating steel in an electricfurnace which consists in applying thereto a slag containing a basicoxid like lime in combination with an acid oxid like silica, the basicand acid components being in such proportion as to form a fluid slag atthe temperature of the melted steel without undue wear on the furnacelining, and While maintaining the metal and slag heated to a meltingtemperature, subjecting the slag to the actionof a reducing agent untilthe oxid of iron is-practically all reduced from the slag and-siliconfrom the slag caused to enter the steel and become incorporatedtherewith. v

12. The method of treating steel in an electric furnace which consistsin applying thereto a slag containing lime and silica in proportions toform a suitablv fluid slag at the melting temperature of the steelwithout undue Wear on the furnace lining, and while maintaining themetal and slag heated to the desired melting temperature,

subjecting the slag to the action of a reducing agent until oxid of ironis reduced from the slag and silicon reduced from the s1l1caof the slag.

In witness whereof I hereunto subscribe my name this twentieth day ofJanuary, A; D. 1911. r

I ALBERT E. GREENE. Witnesses:

GEORGE E. FOLK, Gno. C. DAVISON

